Nested dish plate heat exchangers have been made in the past where a plurality of stacked plates having overlapping peripheral side walls are put together to define hollow fluid passages between the plates, usually with different fluids in heat exchange relationship in alternating spaces between the plates. Usually, a base plate or mounting plate is attached to an uppermost or a lowermost one of the stacked plates, and the mounting plate has holes or fasteners to attach the heat exchanger to a piece of equipment, such as an automobile engine. Oil from the engine passes through openings in the mounting plate and engine coolant passes through other inlet and outlet holes in the mounting plate, or fittings attached to the heat exchanger in order to cool the engine oil in use.
In the nested dish plate heat exchangers made in the past, the plates are usually made of thin material. Also, the plates are often made of aluminum which has inherently lower mechanical strength relative to ferrous alloys, particularly after brazing. A difficulty with this is that some of the dish plates, usually the ones attached to the mounting plate, are prone to fatigue fracture due to vibration, mounting plate deformation, thermal stresses and internal pressure stresses transmitted from the engine to the nested dish plates through the mounting plate, and also from the coolant hoses attached to the heat exchanger. Base plate or mounting plate deformation, in particular, presents a significant problem since mounting plates may tend to form poor braze joints with the lowermost plate in the stack of nested dish plates and are, therefore, prone to failure.
In U.S. Pat. No. 5,927,394 issued to Robert Mendler, et al., an attempt is made to ameliorate the difficulties mentioned above by adding an extra thick reinforcing dish plate below the lowermost regular dish plate. The reinforcing dish plate is formed with a generally flat base portion and has upright tabs formed on its longitudinal and transverse sides which are bent upwards at an angle from the plane of the base portion. A difficulty with this is that the extra reinforcing plate adds height and weight to the heat exchanger. The reinforcing plate also requires a unique and costly die, as well as increased care and handling during assembly and thus adds cost to its manufacture.